textproduct: Quad Cities

KEY MESSAGES

- Areas of rain and thunderstorms this afternoon, with uncertainty on how far north the severe threat (level 2/3 of 5) returns and especially the tornado threat, with main concern along/south of U.S. Highway 34; threat ends near 6 PM.

- Because of the heavy rain this morning in many places and numerous storms still this afternoon (even if elevated), there will be local flash flooding to continue or redevelop, especially across metros.

- Quiet weather will be seen through the second half of the work week, with the pattern becoming active again this weekend and beyond.

UPDATE

Issued at 1135 AM CDT Wed Jun 17 2026

Our focus is now on the assessment of morning storms and their effect on the afternoon activity. While there is a notable imprint on the temperature field, one challenge with this event is that it is far more spring-like than summertime. In other words, the strength of the low pressure (992 mb) will help drive parameter fields by stronger advection than we would typically see in June. As a testament to this is an impressive June temperature gradient across the area with mid to upper 50s north and central to low 80s just south of the CWA.

The surface warm front modulated by outflow from the morning storms is draped just south of the CWA border. Strong WAA aloft and moisture transport are resulting in regularly developing thunderstorms near the 850 mb frontal zone over the I-80 corridor, with mainly a flash flood threat. Also impressive cloud-to-ground lightning even when rain rates diminish some. Near the surface warm front, satellite indicates fairly solid cloud cover near the Iowa/Missouri border. However, some of this is transitioning to towering cumuliform clouds from near Ottumwa southwestward along a confluence axis. We are thinking this may be the start of the afternoon round of storms as it progresses eastward across locations near/south of U.S. Highway 34, and likely some gradual northeast expansion, possibly even near to the I-80 corridor in Illinois.

As upper forcing from a 120 kt upper jet impinges over this area, mature convection should gradually develop. These storms will be at least close to being rooted in the boundary layer, but even if slightly elevated will have severe potential. The parameter space remains favorable for significant severe weather, including hail even though we did not have much with the morning activity. Of greater concern is if rooted in the boundary layer there would be the threat of tornadoes, some potentially significant given a stout parameter gradient (as shown by a forecast STP gradient of 1-6 by 3 PM). Whether that truly manifests into surface-based supercells in our CWA is still an uncertainty.

Now this is not to say there is not a severe, and even a lower end tornado threat, further north toward Iowa City and the Quad Cities, simply because of the dynamics with this system. Dew points in the mid 60s have returned to central Iowa on southeast winds, and continued pressure falls will help keep that low-level theat-a advection increasing ahead of the low pressure. In tandem with effective shear in the 1-6 km layer of 50+ kts, at least some organization for scattered severe is plausible, and we'll have to keep a close eye on the low-levels. As long as storms keep regenerating along this I-80 corridor, it may prevent true low-level warming and CAPE from building up to the I-80 corridor in our CWA.

Confidence is high in any severe weather threat clearing our area near 7 PM. Isolated showers and storms in northwest Illinois may continue to 9 PM before the forcing has pushed east.

SHORT TERM /THROUGH TONIGHT/

Issued at 215 AM CDT Wed Jun 17 2026

Severe weather is expected today as a seasonably strong system moves through the region. This will bring two rounds of storms to eastern Iowa, northwest Illinois, and northeast Missouri: a first round in the morning hours (4-9 AM) and second round in the afternoon hours (12-7 PM). Morning storms are anticipated to have a primary threat of large hail and low damaging wind potential, while afternoon storms will be capable of all hazards, including tornadoes. In addition, heavy rain will lead to localized flash flooding, especially in areas that see repeated rounds of storms.

A strong shortwave will move from the Northern Plains into the Upper Midwest this morning. Pressure heights are near or at the NAEFS climatological minimum for mid-June, while winds aloft are near or at their maximum. This can be seen in a strong (50-60 kts) zonal jet at 500 mb sampled upstream with today's 00Z soundings. As this system translates into the Upper Midwest early this morning, southerly to southwesterly flow across the central Plains will provide warm air advection and moisture, which will amplify with the LLJ towards sunrise. As a result, dewpoints are forecast to rise into the mid to upper 60s within a few hours after sunrise, creating a sharp gradient between the northern and southern halves of the CWA. Lift along this WAA wing will provide the focus for morning convection, with showers and storms across the area.

For the morning, the greatest risk for severe storms is along and south of Interstate 80, though there is some uncertainty given a strong cap over the region. If storms are able to develop, shear magnitude and direction suggests a mixed storm mode with multicell and supercells storms. A favorable severe environment of high lapse rates (7.5-8.5 degC/km) and up to 2000 J/kg of MUCAPE will support a primary risk of large hail. In addition to the risk of large hail, heavy rain will be possible with these these storms. This should be a soaking rain this morning and flash flooding threat should be limited, save for areas that have a long residence time with storms. This would primarily occur with cells that move over the same areas, as storms in this first round will be moving quickly towards the east at 40-50 kts.

By mid- to late morning, these storms will move east into central Illinois, giving the airmass time to recover. At this point, strong southwesterly flow will continue to feed in moisture and instability, providing the energy necessary for the second round of storms. The greatest area of uncertainty is in how much recovery time will be possible, as morning storms and showers could persist longer than anticipated. If the atmosphere is able to recover following morning storms, an environment favoring supercells will develop, leading to the potential for all hazard severe thunderstorms.

Around 12 PM, forcing along the cold front will plow into a region of 2000 (north) to 4000 (south) J/kg of CAPE, providing the forcing necessary for convective initiation. These storms will be fast moving, with a storm motion of 50 kts to the east. Large hail and damaging winds are possible with all storms. Tornado threat will be more limited, with the best low level shear supporting the highest tornado threat in west-central Illinois. These storms will exit into central Illinois around 6-7 PM.

Once these storms move off to our east, CAA advection behind the front will support westerly to northwesterly winds up to 20-25 mph, leading to a breezy night.

LONG TERM /THURSDAY THROUGH TUESDAY/

Issued at 215 AM CDT Wed Jun 17 2026

Several pleasant, mainly dry days will follow our big system today. This will lead to temperatures below normal for highs and lows Thursday and Friday. Dry air should keep any rain threat low, though some energy skirting by aloft could bring some sprinkles or even a tiny thunderstorm as early as Friday night.

Warm begins to spread northward again towards Saturday, as the flow aloft shifts towards a more active zonal flow regime. Models remain consistent in showing a warm front developing over the Midwest Saturday night, and having at least one significant wave of rain and thunderstorms/ potentially an MCS Sunday and Sunday night. There is latitude differences in the latest deterministic guidance, with the GFS shifting that axis a bit south, and the EC and GEM maintaining a more northerly frontal zone. Regardless, that will be the next period for us to focus on for both heavy rainfall and a thunderstorm risk.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1258 PM CDT Wed Jun 17 2026

Scattered storms with MVFR to VFR visibilities continue at KMLI for the next hour or so. Also expect some shower activity at or near KDBQ, KCID, and KBRL at times this afternoon. Additional scattered strong to severe thunderstorms are forecast to develop in a west to east orientation near or just south of KBRL between 19Z to 21Z this afternoon, but only included these as a TEMPO group for now as it is possible that they develop just far enough south to not impact the terminal at all. Another round of isolated storms are possible with the cold front passage between 22Z-01Z this evening for KCID, KDBQ, and KMLI, and a lower potential (around 30%) at KBRL. Ceilings return to VFR behind the storms this evening. Breezy southeast to south winds persist ahead of the cold front then turn westerly behind the front this evening. Gusts should drop off with a small inversion setting up overnight. Wind gusts should pick back up out of the northwest daytime Thursday, with scattered to broken MVFR ceilings moving into KDBQ late tonight and for a few hours Thursday morning at KCID, KMLI, and KBRL. Low-level wind shear develops at most terminals for a few hours this evening.

DVN WATCHES/WARNINGS/ADVISORIES

IA...Flood Watch until 7 PM CDT this evening for IAZ063>068-076>078- 087>089-098-099. IL...Flood Watch until 7 PM CDT this evening for ILZ009-015>018- 024>026-034-035. MO...Flood Watch until 7 PM CDT this evening for MOZ009-010.